4GB RAM Performance Increase

I have a MacBook Pro base model C2D and I was thinking of going up the line to 4GB. I mostly use my computer for movies, internet, photos, and a lot of games. Will this offer much of a performance increase for those kinds of things? Also, where can I get 2x 2GB memory sticks for the MBP for cheap?
I found these; will these work in my MBP? http://cgi.ebay.com/2x2GB-APPLE-MAC...oryZ4601QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

Well, I'll be playing COD2, installing Windows XP soon, (just purchased on eBay for an AMAZING price) and playing games such as BF2 and COD4. So I don't know if it will make a difference but I saw a bunch of these videos of this guy who had a the middle model of MBP's and had 4GB RAM and was playing a bunch of games like COD4 and they looked amazing. That link you sent me had 4 GB RAM for only $99.99!!!! That's incredible!! But I don't know if I'll need it... But I have to admit that is an amazing deal.

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